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Our errors should support basic error properties like message, name and, preferably, stack.… For instance, it may not have name and age properties that are essential for our users.… Our function readUser(json) will not only read JSON, but check (“validate”) the data.… We just need to take care of the name property and don’t forget to call super.… Then name property can be used for such checks.

Examples of valid names: When the name… These names are valid:… Such names are allowed, but there is an international convention to use English in variable names.… Make names maximally descriptive and concise. Examples of bad names are data and value.… Such names say nothing.

Import “as”.We can also use as to import under different names.… A module has either named exports or the default one.… Named exports force us to use exactly the right name to import:… So they prefer to always use named exports.… /user.js' re-exports only named exports, but ignores the default one.

In other words, it should be valid JavaScript.… Error name.… property is exactly the name of the constructor.… And in our case, the absence of name is an error, as users must have a name.… with error name (error constructor name). stack (non-standard, but well-supported) – the stack at the

Named slots.Let’s see how slots work on a simple example.… For rendering purposes, for each <slot name="...… " with the same name in the light DOM.… " attribute is only valid for direct children of the shadow host (in our example, <user-card&… There are two kinds of slots: Named slots: <slot name="X">...

. elem.getAttribute(name) – gets the value. elem.setAttribute(name, value) – sets the value. elem.removeAttribute… (name) – removes the attribute.… But that doesn’t matter: attribute names are case-insensitive.… Name is case-sensitive Name is not case-sensitive Methods to work with attributes are: elem.hasAttribute… (name) – to check for existence. elem.getAttribute(name) – to get the value. elem.setAttribute(name,

Here’s the example with user assigned to a name… We’d like to display the user name using one of these variables, or show “Anonymous” if all of them are… In practice, the zero height is often a valid value, that shouldn’t be replaced with the default.

In the user object, there are two properties: The first property has the name "name" and the… The second one has the name "age" and the value 30.… The dot requires the key to be a valid variable identifier.… Instead of name:name we can just write name, like this:… Also, we could use another variable name here instead of key.

Slot name doesn’t matter. Just any slotted element, but only the element itself, not its children.… These selectors are invalid: Also,… component: The component uses a custom CSS property to style key elements, such as var(--component-name-title… When a developer wants to style a title, they assign --component-name-title CSS property for the shadow

If the string is not a valid number, the result of such a conversion is NaN.… Please note: the string with zero "0" is true Some languages (namely

Custom element name must contain a hyphen - Custom element name must have a hyphen -, e.g… . my-element and super-button are valid names, but myelement is not.… That’s to ensure that there are no name conflicts between built-in and custom HTML elements.… To get the information about custom elements, there are methods: customElements.get(name) – returns… the class for a custom element with the given name, customElements.whenDefined(name) – returns a promise

To see the DOM node class name, we can recall that an object usually has the constructor property.… Sure, the difference is reflected in their names, but is indeed a bit subtle.… “as HTML”: all tags become tags, so we see the bold name.… The second <div> gets the name “as text”, so we literally see <b>Winnie-the-Pooh!… Read-only. nodeName/tagName For elements, tag name (uppercased unless XML-mode).

Despite having the word “XML” in its name, it can operate on any data, not only in XML format.… Please note that open call, contrary to its name, does not open the connection.… given name and value.… ) Gets the response header with the given name (except Set-Cookie and Set-Cookie2).… So, if we want to get an object with name/value pairs, we need to throw in a bit JS.

Object property names are double-quoted also. That’s obligatory.… Namely: Function properties (methods). Symbolic keys and values.… So the objects in participants are empty, because name is not in the list.… JSON.parse.To decode a JSON-string, we need another method named JSON.parse.… Adding a comment to JSON makes it invalid.

Can be created with {}, for instance: {name: "John", age: 30}.… For example, this is entirely valid:

There’s another event named input to track changes of an <input> field, by any means.… Special keys are coded by their names: "Enter", "Backspace", "Tab" etc.… If it’s valid (from 0..9 or one of +-()), then it returns true, otherwise false.… There we can check the new input.value and modify it/highlight the <input> when it’s invalid.

To name some (for historical reasons): AMD – one of the most ancient module systems, initially implemented… There are core features, valid both for browser and server-side JavaScript.… As you can see, when 1.js changes the name… For instance, this import is invalid:… The resulting file is minified (spaces removed, variables replaced with shorter names, etc).

Please note, without separate blocks there would be an error, if we use let with the existing variable name… It can access the outer variables and so can return the full name.… -- ```js let phrase = "Hello"; function say(name) { alert( `${phrase}, ${name}` );… It has a single property: name, the function argument.… We called say("John"), so the value of the name is "John".

These methods are only used in the specification, we can’t call them directly by name.… For every internal method, there’s a trap in this table: the name of the method that we can add to the… target – is the target object, the one passed as the first argument to new Proxy, property – property name… Validation with “set” trap.Let’s say we want an array exclusively for numbers.… After the wrapping, the access is lost to properties of the original functions, such as name, length

To find a particular cookie, we can split document.cookie by ;, and then find the right name.… Technically, name and value can have any characters.… The name=value pair, after encodeURIComponent, should not exceed 4KB.… The function getCookie(name) returns the cookie with the given name:… Name/value must be encoded. One cookie may not exceed 4KB in size.

Backreference by name: \k<name>.If a regexp has many parentheses, it’s convenient to give them… names.… To reference a named group we can use \k<name>.… In the example below the group with quotes is named ?

digits) getMonth() Get the month, from 0 to 11. getDate() Get the day of month, from 1 to 31, the name… If the format is invalid, returns NaN.

Behavior Driven Development (BDD).Let’s start with a technique named Behavior Driven Development or,… Let’s do the same for invalid values of n. Let’s first add the behavior to the spec(!)

The browser ignores its contents, only checks for syntax validity, but we can access and use it in JavaScript… First, its content can be any valid HTML, even if it normally requires a proper enclosing tag.… Usually, if we try to put <tr> inside, say, a <div>, the browser detects the invalid

also supported. options – optional object: fatal – boolean, if true then throw an exception for invalid

Let’s use them for validation of an input field.… Modern HTML allows us to do many validations… For instance, let’s make the visitor unable to leave the input if the value is invalid:

The submit event triggers when the form is submitted, it is usually used to validate the form before

Or, maybe, everything is all right with the site, but the response is not valid JSON.… But if any of the promises above rejects (a network problem or invalid json or whatever), then it would

It accepts 25:99 as the time (as 99 minutes match the pattern, but that time is invalid).

form field with the given name and value, formData.append(name, blob, fileName) – add a field as if… name), as it were a name of the file in user’s filesystem, formData.delete(name) – remove the field… with the given name, formData.get(name) – get the value of the field with the given name, formData.has… , value) formData.append(name, blob, fileName) formData.set(name, value) formData.set(name, blob, fileName… Other methods are: formData.delete(name) formData.get(name) formData.has(name) That’s it!

For instance, a function’s name is accessible as the “name” property:… have a name.… Adding such a name also did not break anything.… Named Function Expression form.… Here we covered their properties: name – the function name.

A generated URL (and hence the link with it) is only valid within the current document, while it’s open… clickable HTML-link, we don’t call URL.revokeObjectURL(link.href), because that would make the Blob url invalid

Name a variable by its type: str, num… Give them a try.… Sure, the variable name still means something.… …But what if there are no more such names?… The name that can be named is not the eternal name.… Reuse names.Once the whole is divided, the parts need names. There are already enough names.

That’s a so-called “named collection”: it’s both named and ordered.… When we have a form, then any element is available in the named collection form.elements.… In that case, form.elements[name] is a collection.… is still available under the old name (as well as under the new one).… Form elements are available as form.elements[name/index], or can use just form[name/index].

It provides convenient methods for search parameters: append(name, value) – add the parameter by name… , delete(name) – remove the parameter by name, get(name) – get the parameter by name, getAll(name) –… get all parameters with the same name (that’s possible, e.g. ?… user=John&user=Pete), has(name) – check for the existence of the parameter by name, set(name, value… ) – set/replace the parameter, sort() – sort parameters by name, rarely needed, …and it’s also iterable

The name argument is a name of the event, optionally followed by additional arguments with event data… name.… It will be called when an event with the given name triggers, and get the arguments from the .trigger… …And the method .off(name, handler) that removes the handler listener.… Technically, there’s an _eventHandlers property that stores an array of handlers for each event name,

The email format is: name@domain. Any word can be the name, hyphens and dots are allowed.… <name> immediately after the opening paren.… parentheses the reference will be $<name>.… <name>...).… $<name>.

Our new function can be called by its name: showMessage().… Naming a function.Functions are actions. So their name is usually a verb.… Ultrashort function names Functions that are used very often sometimes have ultrashort names… Generally function names should be concise and descriptive.… Function naming: A name should clearly describe what the function does.

But sometimes we want same-named symbols to be same entities.… Symbol.keyFor.We have seen that for global symbols, Symbol.for(key) returns a symbol by name.… Symbols are created with Symbol() call with an optional description (name).… Symbols are always different values, even if they have the same name.… (creates if needed) a global symbol with key as the name.

In a browser it is named window, for Node.js it is global, for other environments it may have another… name.… Recently, globalThis was added to the language, as a standardized name for a global object, that should… The global object has a universal name globalThis.… …But more often is referred by “old-school” environment-specific names, such as window (browser) and

For instance, we have a user object with name and surname:… For instance, if we want to forbid too short names for user, we can have a setter name and keep the value… So, the name… Technically, external code is able to access the name directly by using user._name.… Imagine we started implementing user objects using data properties name and age:

of a class expression: Similar to Named… Function Expressions, class expressions may have a name.… If a class expression has a name, it’s visible inside the class only:… Computed names […].Here’s an example with a computed method name using brackets [...]:… For instance, let’s add name property to class User:

Also, there’s a global variable named… …That’s unless we declare a JavaScript variable with the same name… Please don’t use id-named… There may be naming conflicts.… ) returns elements with the given name attribute, document-wide.

fileParts – is an array of Blob/BufferSource/String values. fileName – file name… As File inherits from Blob, File objects have the same properties, plus: name – the file name, lastModified… In addition to Blob methods and properties, File objects also have name and lastModified properties,

Now it’s easy to see that the range 56499-55349 is invalid: its starting code 56499 is greater than the

The value of Reference Type is a three-value combination (base, name, strict), where: base is the object… . name is the property name. strict is true if use strict is in effect.

There are two conventions though: They are named with capital letter first.… For instance, new User(name) below creates an object with the given name and the method sayHi:… Constructor functions or, briefly, constructors, are regular functions, but there’s a common agreement to name

We can use any other variable name in place of rest, just make sure it has three dots before it and goes… In the simplest case, that’s a list of variable names in {...}.… If we want to assign a property to a variable with another name, for instance, make options.width go… into the variable named w, then we can set the variable name using a colon:… example above the property width goes to w, property height goes to h, and title is assigned to the same name

Despite being named an “object store”, primitives can be stored too.… name is the store name, e.g.… Get the store object using transaction.objectStore(name), at (2).… This required an additional data structure, named “index”.… The syntax: name – index name, keyPath

E.g. we have a code string let varName = "value", and we need to read the variable name from… We’ll look for variable name using regexp \w+.… Actually, JavaScript variable names need a bit more complex regexp for accurate matching, but here it